Mackintosh performed with the Royal National Theater. Breaking into television, he appeared on such series as Doctor Who, The Secret Life of Adrian Mole, The Bill, Maigret, Poirot, and Cadfael. Film credits include Memphis Belle (with Matthew Modine and Harry Connick Jr., in the small role of a rookie radioman who is shot down), Princess Caraboo, Lock Stock and Two Smoking Barrels, The Jacket, and Underworld: Evolution (as vampire archivist Tanris). He also appeared in the mini-series Prime Suspect 5: Errors of Judgement (as ruthless drug dealer "The Street") and Our Mutual Friend (as John Rokesmith).